In the related art, a turbocharger is known which compresses air and supplies the air as combustion air for an internal combustion engine into cylinders. For example, the turbocharger is widely used in 2-stroke low-speed engines such as marine diesel engines and power generation diesel engines. In this turbocharger, a compressor for compressing the combustion air and a turbine serving as a drive source of the compressor are connected to each other via a rotor shaft, and are accommodated inside a casing. In this manner, both of these are integrally rotated. For example, the turbine driven using exhaust gas discharged from the internal combustion engine as a drive source.
As one type of the turbocharger, a hybrid turbocharger known in which an electric motor is connected to the rotor shaft (for example, refer to PTL 1). Similarly to a normal turbocharger, the hybrid turbocharger compresses the air, and supplies the air as the combustion air into the cylinders of the internal combustion engine. In addition to this function, the hybrid turbocharger drives a rotor shaft by using excess exhaust gas discharged from the internal combustion engine so that the electric motor generates electric power.
In addition, as another type of the turbocharger, an electric assist turbocharger is known in which a motor is connected to a rotor shaft (for example, refer to PTL 2). In the electric assist turbocharger, the motor is miniaturized by omitting a power generation function of an electric motor generator used for the hybrid turbocharger and focusing on an electric motor function.